Alkaline pulping of lignocellulose in the presence of oxygen to produce pulp, vanillin, and other oxidation products of lignin substance



H. B. MARSHALL ET AL 2,686,120 PIN OCELLULOSE IN THE PRESENCE OF OXYGENT0 PRODUCE PULP, VANILLIN, AND OTHER F LIGNIN SUBSTANCE Aug. 10, 1954ALKALINE PUL G OF LIGN OXIDATION PRODUCTS 0 2 Sheets-Sheet 1 Filed Jan.14, 1952 Aug. 10, 1954 Filed Jan. 14, 1952 OF OXYGEN T0 PRODUC OXIDATIONPRODU E PULP, VANI CTS OF LIGNI IN THE PRESENCE LLIN, AND OTHER NSUBSTANCE 2 Sheets-Sheet 2 I a M495 flLL Patented Aug. 10, 1954 ALKALINEPULPING OF LIGNOCELLULOSE IN THE PRESENCE OF OXYGEN TO PRO- DUCE PULP,VANILLIN, AND OTHER 'OXI- DATION PRODUCTS "OF LIGNIN SUB- STANCE HarryBorden Marshall, Toronto, OntarioQand Charles Alfred Sankey,

Canada, as'signors to pany Limited, Thorold St. Catharines, Ontario,

The Ontario Paper Com- Ontario, Canada Application January 14, 1952,Serial No. 266,354.

5 Claims. (01. 929) This invention relates to the pulping oflignocellulosic materials. It also relates to the production ofoxidation products, including vanillin, from fibrous lignin-containingsubstances, in-

cluding wood, and the formation of the same,

during an alkaline pulping operation, and is a continuation-in-partofapplication S. N. 700,018, filed September 28, 1946, now abandoned, andentitled Method for Pulping Lignocellulose Materials and simultaneouslyProducing Oxidation Products Therefromff In our Patents Nos. 2,516,827,issued July 25, 1950 and No. 2,544,999, issued March 13, 1951, therewere disclosed methods whereby air or oxygen could be employed to efiectthe production of vanillin at highly satisfactory yields fromlignin-containing substances. The lignin-containing substances referredto therein were characterized in that the lignin content was availablefor oxidation either in solution (for example,

sulphite waste liquor) or in a substantially fine state of subdivision(for example, wood meal).

The raw or starting material used in the above mentioned patents didnot, therefore, have the full natural fibrous structure characteristicof an original plant material but, on the contrary, the

lignin substance had been removed from such original natural environmenteither in the form of a soluble derivative (for example, in sulphitewaste liquor) or, in the alternative, made available for chemical actionby cutting, abrading or comminution to the extent that the originalfibrous structure of the plant material was substantially destroyed (forexample, wood meal).

By fibrous lignocellulosic material" we have reference to and mean alignocellulosic material, the natural structure of which is of a fibrouscharacter and, furthermore, that such fibrous character has not beensubstantially impaired by abrading, comminution, other drastic cutting,or process of masceration or the like prior to its use as a raw orstarting material for our present invention. In particular we havereference to the materials which are still of a lignocellulosiccharacter as are discussed by G. S. Witham, Sr., in Modern Pulp andPaper Making, Reinhold Publishin Corp, New York, 1942, Chapter 2, and byJ. N. Stephenson (Editor in Chief) in Pulp and Paper Manufacture; vol.1, Preparation and Treatment of Wood Pulp, McGraw 2 Hill Book Co. IncNew' York, 1950, Chapter 1. It will thus be understoodthat previouslypulp ed materials such as are described byWitham and by Stephenson areno longer lignocellulosicin character and do not fallwithin thedefinition of the raw or starting material employed by us. Qurinvention,therefore' relates to the class of material here definedand when in thespecification and claims wemake reference to fibrous lignocellulosicmaterials we mean andhave reference only to the class ofmaterials aboveded .7, V. V,

The production of wood pulp by chemical processes from fibrouslignocellulosic materials is specifically directed towardtheprodu'ctionof an end product of fibrous character and having such otherqualities as are requisite for wood pulp. For examplefi'woodmay bechipped into units sufficiently small so that proper penetration ofchemicals into theunit chip can be obtained under pulping conditions,but also sufliciently large so that'the fibrous structure of the wood isnot unduly damaged. During the pulping operation,'the lignin and otherincrusting materials of wood are subjected to the chemical action of thepulping chemicals so that the fibrous units in the wood become readilyseparable to form a wood pulp; 'This balance in particle size of 1fibrous lignocellulosic units, to permit adequate chemical actionfortheproduction of afibrous end product,"is' the essence of the art ofpulping lignocellulosicmaterials." We haveijnowidiscovered that it ispossible in one single operation by the following process which we haveinvented, to obtain from'fibrous lignocellulosic materials, both afibrous pulp and oxidation products ,of lignin, including vanillin.Although vanillin is a principal oxidation product from the ligneouscontent of the lig'nocellulosicmaterials employed by us when treated inaccordance with our present invention, other oxidation products are alsoformed. Among such other products formed when soft woods are treated inaccordance with our invention, we have identified acetovanillone,vanillic acid, and guaiacol; when hard woods areemployed,syrin'galdehyde and acetosyring one are formed in addition; when certainfibrous annual crop materials such as bagasse," wheat straw, 'fia'xstraw, soyabean stalks and cat hulls areemployed, both vanillic 3 andsyringic derivatives, as well as parahydroxy bemaldehyde have beenidentified in addition to vanillin.

In our Patent No. 2,516,827 referred to above, the efiluent fromalkaline chemical processes for producing wood pulp such as residualkraft liquor and residual soda liquor were cited as examples oflignin-containing substances to which the disclosures of that patentwere applicable. The conditions for the production of vanillin accordingto the disclosures contained in the said patent were those of oxidationin an alkaline medium. The pulping process which we employ coincident toand simultaneously with the production of vanillin and other oxidationproducts from lignin substance is, therefore, an alkaline chemicalprocess for producing wood pulp. We have also discovered that not onlymay simultaneous pulping action and alkaline oxidation of lignin tovaluable end products be effected simultaneously, but also that byemploying our present invention, the yields of vanillin aresubstantially increased over those which would be obtained were thepulping operation and the alkaline oxidation of lignin conducted asseparate steps in series, i. e., in accordance with the known art ofalkaline pulping, followed by the use of the invention disclosed in ourPatent No. 2,516,827. Thus, in a process involving the use of woodchips, if a sample of such chips be divided into two portions, the firsttreated according to our present invention, and the second pulped by aknown alkaline pulping process, for example, the soda process, and theresidual liquor from the latter then subjected to oxidation inaccordance with our previous invention as described in our Patent No.2,516,827, there will result a substantially higher yield of vanillin bythe former procedure.

The properties of any wood pulp are dependent on the pulping methodemployed and there are characteristic differences between wood pulpsproduced by different methods of pulping. In the case of any one pulpingmethod, a wide range of pulp quality may also be obtained dependent uponthe pulping conditions actually employed. The variation of suchconditions in any given pulping process to produce a desired end resultconstitutes the basis of the art of chemical wood pulping.

The oxidizing conditions employed in our invention modify the pulpingprocess from that which would obtain according to the well knownalkaline pulping processes with the same pulping chemicals and the sametemperature-pressure-time cycle. In general we have found that the rateand degree of pulping in accordance with our invention are less thanwhen the oxidizing conditions, as herein described, are not employed.The yield of vanillin and of other oxidation products of ligninsubstance is also dependent on the reaction conditions. To assure both asatisfactory pulping action and a satisfactory yield of oxidationproducts, we recommend and prefer a digesting temperature in the range150 C. to 200 C. The severity of oxidation of lignin substance isdetermined by temperature, partial oxygen pressure, time of reaction,and by the extent of circulation or mixing of the digester contents.

For a satisfactory yield of oxidation products in.

the above temperature range, we recommend and prefer a reaction time ofnot more than four hours and conditions of digester pressure in therange 50 to 300 lbs. per square inch, the partial pressure of oxygenbeing that autogenically de veloped when using air as the source ofoxygen under the above conditions. The essential criteria of thereaction conditions of our invention are, however, first, that a fibrouswood pulp is produced and, second, that one or more of the oxidationproducts of lignin substance, as here-in stated, are simultaneouslyproduced. It will be obvious to anyone skilled in the wood pulping artthat a wide variety of conditions may be employed from which a selectionwill be made with pulp quality and yield of oxidation products in mind.Examples of the application of our invention will be given whichdemonstrate that under certain conditions a wood pulp of useful qualitymay be obtained. Our invention is not limited to such conditions,however, but includes any conditions where oxidation of lignin tomaterials including vanillin and an alkaline chemical pulping processare combined in a single reaction.

Figure 1 shows in diagrammatic form an apparatus which we have used insome of our experiments and comprises a bomb I, into which the reactantsare introduced, a cover 2, containing an opening 3, leading to acondensing system 4, in which vapours from the bomb may be condensed andreturned thereto by reflux through the opening 3, the condenser systemterminating in the control relief valve 5, which limits the maximumpressure in the reaction system to a predetermined value. In the bottomof the bomb I, is a porous plate 6, beneath which air or oxygen may beintroduced and which serves as a gas difiusing means by which air oroxygen enters the reaction zone in a finely divided state. The air oroxygen is supplied from a pressure cylinder 7, through valves 8, 9,which control the pressure and rate of discharge from the cylinder intothe gas diffusing means by tube III.

The bomb is also equipped with a pressure gauge II, and a thermometerwell I2, containing a thermometer 43, by means of which the pressure andtemperature of the reaction may be noted. The bomb I, may be heated byany convenient means, for example, a gas flame I4. A relief valve I5, isprovided for general pressure reduction.

Modifications of the equipment as described herein which will producethe combined action of pulping lignocellulosic materials and of theproduction of vanillin and other oxidation products therefrom will beapparent to those skilled in the art. For example, the pulping liquormay be circulated through the digester and subjected to the action of agas containing oxygen, as described herein, in a vessel which comprisesa portion of the circulation system external to the digester. Suchmodifications of the apparatus are to be considered as lying within thescope of our invention.

Apparatus for the practice of our invention utilizing a circulationsystem external to the digester and carried out during the pulping operation is illustrated in Figure 2. In this figure, the digester IilImay be of any design normally used for cooking by alkaline pulpingprocesses. For example, as illustrated, it may have a removable top I02for chip loading; a set of false bottom strainer plates I03 fastened tothe digester wall and forming an annular space around the internalcircumference of the bottom of the digester for liquor withdrawal; and adigester discharge valve I04. Any suitable heating system either director indirect may be employed. In Figure 2 an external indirect heatingsystem is illustrated as an example and comprises the pipe I05, theliquor circulating pump I96, the

. and estimation of vanillin in Buckland, Tomlinson andpipe I01 leadingto the bomb or heater-reactor I03 in which suitable means for heatingare provided, for example, the steam coil I09. The liquor from theheater-reactor I 03 is returned to the digester through the pipe I It.The treatment of the liquor with a finely dispersed gas containing freegaseous oxygen is accomplished the heater-reactor I08 in which agitationis provided by the turbo-mixer I II driven by the the motor H2. Air issupplied from the compressor H3 through the tank EM and after regulationas to pressure and rate of air flow by valves H5, H6 enters theheater-reactor Hi8 through the pipe III and is dispersed therein by theturbo-mixer HI which is placed over the baffle I IS, the latter servingto keep the air from the heating zone around the coil I 09. It isunderstood, of course, that any suitable means of agitation may beemployed. The bomb or heaterreactor I08 as in the case of the device,shown in Figure 1, is provided with a cover I I9 provided with anopening I20, leading to a condensing system I EI terminating in thecontrol relief valve I22. Pressure gauge I23, thermometer well I24containing thermometer I25 and relief valve I26 are all provided as inthe device shown in Figure 1 and for similar purposes.

By the practice of our present invention vanillin is present as analkali salt in the liquor residual from the alkaline pulping operationand may be isolated therefrom and purified by known means. Othermaterials co-produced and capable of forming an alkali salt aresimilarly present in the liquor in the form of such alkali salt andknown means may also be applied to their isolation and purification.

The following description of experiments which have been performed by uswill serve to illustrate the application of our invention and it is tobe understood that our invention is not limited to the materials andconditions described in these experiments which are to be considered asexamples only. The apparatus in which the experiments were carried outwas of small capacity and therefore required a higher ratio of liquor tolignocellulosic material and larger quantities of chemicals than wouldnormally be necessary in commercial units. It is well known that thiskind of relation exists between experimental cooking in small digestersand commercial operation in the known chemical processes for producingwood pulp. The experimental data are to be interpreted with this inmind.

The determination of lignin in the fibrous raw materials used for ourprocess was in accordance with standard method T13m-43 of the TechnicalAssociation of the Pulp and Paper Industry (U. 8.). All yields ofmaterials when expressed on a lignin basis have reference to lignin asso determined.

In the evaluation of Wood pulps the methods employed were the standardmethods of the Technical Association of the Pulp and Paper Industry (U.S.) for example, method T222m-45 for lignin in wood pulps, T227m-43 forfreeness (Canadian standard), T205m-42 for forming hand-sheets forphysical tests of pulp, T220m-42 for physical testing of pulphandsheets, and so on.

In determining the presence and yield of vanillin and variousco-products, the following techniques were employed. Where interferencewith syringyl derivatives did not apply, we used a gravimetric procedureinvolving the separation the form of its mnitrobenzoyl hydrazone. Thisis described by Hibbert, Can. J. Re-

search 163, 54 (1938), but employing etherqas a solvent in place oftrichlorethylene as described in the above reference. Alternatively, weused a spectrometric method of analysis according to the general methodof Lemon, Ind. Eng. Chem, Anal. Ed, 19, 846 (1947). This is a rapidprocedure which gives an overall measure of substances which arespectrometrically active at approximately 3500 A., the vanillin beingthe principal substance present which is so active.

In the case of materials where syringyl derivatives were present, theabove method of Lemon was also applied but here the result gives anoverall indication of the total simple aromatic cleavage products oflignin as formed in the reaction. In the identification of specificcompounds present among the cleavage products so formed, we haveemployed chromatographic methods as described by Stone and Blundell,Anal. Chem., 23, 771 (1951). Identification of vanillin, syringaldehyde,parahydroxy benzaldehyde, acetovanillone and acetosyringone were made bythis technique.

Example 1 One hundred grams, Wet weight, of spruce chips containing 41%moisture were heated with 60 grams sodium hydroxide dissolved in onelitre of water in the previously described apparatus. Throughout theheating cycle a steady fiow of compressed air was introduced through thediffuser, the valve 5 being adjusted to relieve .gas at 110-115 lbs. persquare inch pressure, the air flow as discharged being adjusted to 13.4cu. ft. per hour. The apparatus reached a final observed temperature of168-170" C. in approximately 25 minutes and was maintained thereat for 3hours. No catalyst or special oxidizing agent such as copper sulphatewas present. At the conclusion of this treatment the air fiow was turnedoff, the system cooled to a lower temperature than its boiling point atatmospheric pressure and the pressure reduced to that of the atmosphereby the relief valve I5.

The contents of the apparatus were emptied, the liquid portion separatedby filtration, and the solid residue (soft chips and pulp) washed withseveral small portions of water which were added to the filtrate.

An aliquot portion of the filtrate was analyzed for vanillin and theamount so determined correlated with the lignin content of the originalwood chips. On this basis a yield of 15 vanillin was obtained.

The soft chips and pulp as separated were subjected to a simpledisintegration by stirring into a fibrous wood pulp. The lignin contentof this pulp was 5%. The pulp was brownish in coiour, had a freeness of748 and handsheets prepared from it had a burst factor of 41.5 and tearfactor of 158. These qualities indicate a usable pulp.

An additional sample of g., wet weight, of the same spruce chips washeated in the apparatus with 60 grams sodium hydroxide dissolved in 1litre of water and subjects to the same temperature-pressure-time cyclebut without air flow. At the conclusion of the experiment the liquidportion was separated by filtration and the solid residue (soft chipsand pulp) washed as before.

An aliquot portion of the filtrate when analyzed indicated a yield of 1%vanillin, based on the lignin content of the spruce chips.

The residue was easily disintegrated into a fibrous wood pulp whichoil-analysis contained 4% lignin. The pulp was somewhat less brownish incolour than that previously described, had a freeness of 701 andhandsheets prepared from it had a burst factor of 48.5 and a tear factorof 1'78.

It will be noted that in the last described above experiment the pulpingcondition parallel those of the conventional soda pulping process exceptthat the amount of alkali employed is substantially higher.

Example 2 Experiments similar to Example No. 1 were performed with thesame spruce chips in which the alkali was 60 grams sodium hydroxide plus30 grams sodium sulphide dissolved in 1 litre of water.

When subjected to air flow the vanillin content of the resultant liquorcorresponded to a yield of 12.5%, based on the lignin content of theoriginal wood chips. The corresponding pulp was of a brown colour, had alignin content of 4%, and after disintegration a freenessof 794.Handsheets had a burst factor of 52.0 and a tear factor of 177.

In the experiment without air the residual liquor had a vanillin contentcorresponding to 2% of the original lignin content of the spruce chipsand the resultant pulp a lignin content of 1.5%; freeness of 705; burstfactor of 39.0 and a tear factor of 233.

It will be noted that in the last described above experiment the pulpingconditions parallel those of the conventional kraft pulping processexcept that the amount of alkali is substantially higher.

E sample 3 A sample of spruce chips was treated as in Example No. 1except that the valve 5. was adjusted to relieve gas at 250 lbs. persquare inch pressure. The air flow, as before, was adjusted to 13.4 cu.ft. per hour and the observed temperature was approximately 170 C.

In the residual liquor there were determined vanillin to the amount of16.8% of the original Our invention may also be applied to hard- 7woods. As is known, the ligneous content of hardwood is more complicatedthan that of soft woods and the oxidation products of hardwood lignininclude compounds which are analogues of vanillin and its relatedcompounds. The application of our invention to hardwoods producestherefore more complicated mixtures of oxidation products.

Example 4 A sample of poplar chips equivalent to 60 grams dry weight wassubjected to a heating cycle as per Example 1. The valve 5 was set torelieve pressure at 110-115 lbs. per square inch. The observedtemperature was approximately 171 C., the airflow 13.4 cu. ft. per hour.

The pulp produced had a freeness. of 616. Handsheets prepared from ithad a burst factor of 25.5 and a tear factor of 80.

In the residual liquor were identified vanillin, syringaldehyde,acetovanillone, and acetosyringone. Owing to the complicated characterof the mixture, yields of each of the above were not determined. Thecombined amounts of vanillin and syringaldehyde were approximately 13.3%of the lignin in the poplar chips.

It will be noted that the above example illustrates the application ofour invention to hardwoods.

Our invention may also be applied to annual crop lignin-containingmaterial which is characterized in its natural state by a fibrousstructure, for example, bagasse, wheat straw, flax straw, soya beanstalks, oat hulls and the like. The ligneous content of such materialsdiifers from that of wood substance and the particular oxidationproducts which are formed depend both as to their nature and quantity onthe fibrous raw material treated in accordance with our invention. It isa common characteristic of all such materials, however, that theoxidation products include vanillin. Other materials have beenidentified among the reaction products as noted in the followingexamples. Just as the quality of pulp obtainable from wood chips isdependent upon the wood species pulped, so is the quality of the pulpobtainable from annual crop fibres dependent upon the species of suchannual crop material pulped. When such materials are used in accordancewith our invention, we have found that the rate and degree of pulpingare less than when the oxidizing conditions herein described are notemployed. An analogous situation, however, maintains to that in the woodpulping art in that a skilled operator can readily make a selection fromthe wide variety of possible conditions to combine the objectives ofsatisfactory pulp quality and good yield of vanillin plus otheroxidation products.

Example 5 A sample of wheat straw equivalent to grams dry weight,containing 16.9% lignin and 7.6% moisture, was heated with 120 gramssodium hydroxide dissolved in 2 litres of water in an apparatus aspreviously described. The apparatus reached a final observed temperatureof 170 C. in 12 minutes and was maintained thereat for 90 minutes.Throughout the reaction compressed air was introduced through thediffuser, valve 5 being adjusted to relieve gas at lbs. per square inch,the air flow as-discharged being adjusted to 13.4 cu. ft. per hour. Nocatalyst or special oxidizing agent such as copper sulphate was present.

As a result of the above treatment the residual liquor contained simplearomatic derivatives from lignin, spectrometrically determined,corresponding to 15.2% of the original lignin content of the wheatstraw. Chromatographic analysis indicated a yield on a lignin basis of5.3% vanillin, 6.2% syringaldehyde, and 0.9% parahydroxy benzaldehyde.Acetovanillone and acetosyringone were identified by chromatographicmethods but were not quantitatively determined.

A straw pulp was removed from the reaction vessel in an amountcorresponding to 34% yield on the original straw. This pulp had afreeness of 299, a burst factor of 31 and a tear factor of 82.

Example 6 We have also applied our invention to bagasse, flax straw, oathulls, and soya bean stalks with experimental conditions and yields asper table 160 C. in 11 minutes and was maintained therebelow: at for 180minutes. The pressure was maintained Whole Oat Whole Flax- Soya BeanFresh-dried Sugar Hul seed Straw Stalks cane Bagasse Raw Material:

Moisture, Percent 9.5.. 6.4.

Lignin, Percent 15.5 17.2. Reaction Conditions:

Dry weight fibrous raw material, g 120 120- 120 120.

Weight Alkali 120 g. NaOI-L. 120 g. NaOlL- 120 g. NaOH 120 g. NaOH plus60 g. NazS.

Final Temperature 170 C. Time to Final Temperature, min. 13 13. Time atFinal Temperature, rnin 60. Gas Relief Pressure p. s. 1. gauge 135. Rateof Gas relief cu. ft./hr 13.4. Aromatic Reaction Products:

3500's (see note 1) 14.5%. Chromatographic analyses- Vanillin 1.7%.Syringaldehyde 2.2% Parahydroxybenzaldehyde 0.9%. Pulp Properties:

Yield, Percent 38 21 36. Freeness (see note 11).... 215 437. Burstfactor. do 7.4 (see note 2).. 26.4. Tear factor do 36 (see note 2)...86.

Note :c.Determined speetrornetrically as hereinbefore described. Notey.'lhe pulp had the appearance of typical flax pulp was required, aswith normal flax pulp, before it could be reduced to a condition wherehandsheets could be formed. Procdid not form satisfactory handsheets.

100, burst factor 12, and tear factor 37.

over-cooked at the temperature employed in the experiment described.

at 110 lb. per square inch, the airflow being ad- The known art ofalkaline pulping of fibrous lignocellulosic materials is normally basedon the use of a caustic alkali, for example, with sodium hydroxide orsodium hydroxide plus sodium sulphide as the active alkaline pulpingagent. Certain fibrous lignoceliulosic materials can, however, accordingto the known art, be pulped under less severe conditions of alkalinity,for example, pulping of straw by lime as the active alkali is well known(see, e. g., G. S. Witham, Sn, Modern Pulp and Paper Making, ReinholdPublishing Corp, New York, 1942, p. 41). In this case the pulp producedis a much more crude product than that which would be made from the samestraw when a caustic alkali is employed and tins is well known in thepulping art. Our invention can, however, be employed for alkalinepulping processes where less severe alkalinity than is typical of theuse of caustic soda with or without the copresence of sodium sulphide isemployed. As already noted, according to the practice of our invention,the pulping action is less severe under a given condition of alkalinitythan is normal for conditions where the oxidizing features of ourinvention are not employed. For this reason a usable pulp will not beproduced in accordance with our invention if the conditions ofalkalinity are insumcient to promote pulping according to the known artof alkaline pulping, for example, a cook of wood chips using lime onlyas the active alkali will result in failure to produce a usable pulpboth under normal conditions of alkaline pulping and when our inventionis employed under similar conditions. The application of our inventionis therefore limited to conditions of alkalinity and the use of alkalissuch that a pulping action is obtained according to the known art ofalkaline pulping. The following example illustrates the application oflime base cooking to whole wheat straw.

Example 7 129 grams equivalent dry weight of the same wheat straw usedin Example 5 was heated with 2 litres of water to which lime had beenadded equivaient to 84 rams calcium oxide. The apparatus reached a finalobserved temperature of The test data are for a mixture 25% soya Thesoya bean pulp was justed to 13.4 cu. ft. per hour.

As a result of the above treatment a straw pulp was produced suitablefor use in strawboard manufacture. The total simple aromatic derivativesfrom lignin, spectrometrically determined corresponded to 6.0% of theoriginal lignin content of the wheat straw. By chromatographic analysisthe following compounds were identified as being produced: vanillin,acetovanillone, syringaldehyde, acetosyringone, parahydroxybenzaldehyde.

When in the specification the word pressure is used, it is to beunderstood that we refer to gauge pressure and not absolute pressure.

We are aware that this invention may be embodied in other specific formswithout departing from the substance thereof and it is, therefore,desired to comprehend within the invention such modifications as may beembraced within the claims and the scope of the invention.

What we claim as our invention is:

l. A process for simultaneously producing from wood chips a fibrous pulpand a vanillin product, which process consists essentially of digestingsaid wood chips in an alkaline pulping liquor at a temperature of C. to200 C. to produce a pulp, continuously passing into the digestionmixture during the pulping step, a finely dispersed gas containing freegaseous oxygen and recovering said vanillin product, said alkalinepulping liquor containing as the sole essential components, water and analkaline pulping reagent selected from the group consisting of sodiumhydroxide and a mixture of sodium hydroxide and sodium sulphide.

2. A process for simultaneously producing from fibrous lignocellulosicmaterial a fibrous pulp and products of oxidation of lignin substanceincluding at least one of the group of compounds consisting of vanillin,acetovanillone, syringaldehyde, acetosyringone, parahydroxybenzaldehyde, said lignin oxidation products being present in the formof their appropriate alkaline derivatives, which process consistsessentially in digesting said material in an aqueous alkaline pulpingliquor at a temperature of 150 C. to 200 C. to produce a pulp,continuously withdrawing said liquor from the digester during thepulping step, continuously passing into said withdrawn liquor a finelydispersed gas containing free gaseous oxygen, continuously recirculatingto the digester during the pulping step said liquor into which said gashas been passed and recovering from said liquor at least one of the saidoxidation products of lignin substance.

3. The process of claim 2 in which the aqueous alkaline pulping liquorcontains as its active pulping agent an alkali selected from the groupconsisting of sodium hydroxide and a mixture of sodium hydroxide andsodium sulphide.

4. A process for simultaneously producing from fibrous lignocellulosicmaterial a fibrous pulp and a vanillin product which process consistsessentially of digesting said material in an alkaline pulping liquor ata temperature of 150 C. to 200 C. to produce a pulp, continuouslywithdrawing said liquor from the pulping step, continuously passing intosaid withdrawn liquor a finely dispersed gas containing free gaseousoxygen, continuously recirculating, to the pulping step, said liquorinto which said gas has been passed, and recovering a vanillin product.

5. The process of claim 3 in which the lignocellulosic material is woodchips.

References Cited in the file of this patent UNITED STATES PATENTS NumberNumber Name Date Summers Jan. 3, 1899 Kellner Nov. 1, 1904 Lucas Dec.17, 1929 Seidel et al May 12, 1931 Richter Nov. 10, 1931 Ross Aug. 15,1933 Kipper Jan, 8, 1935 Richter July 2, 1935 Plant May 20, 1941 DreyfusFeb. 19, 1946 Salvesen Jan. 13, 1948 Marshall at al July 25, 1950Marshall et al Mar. 18, 1951 FOREIGN PATENTS Country Date Great BritainMay 20, 1941 OTHER- REFERENCES Wise, Wood Chemistry (1944) pages 718,717 Reinhold, N. Y., publisher.

Serial No. 318,386, Freudenherg (A. P. C.) puband 325.

1. A PROCESS FOR SIMULTANEOUSLY PRODUCING FROM WOOD CHIPS A FIBROUS PULPAND A VANILLIN PRODUCT, WHICH PROCESS CONSISTS ESSENTIALLY OF DIGESTINGSAID WOOD CHIPS IN AN ALKALINE PULPING LIQUOR AT A TEMPERATURE OF 150*C. TO 200* C. TO PRODUCE A PULP, CONTINUOUSLY PASSING INTO THE DIGESTIONMIXTURE DURING THE PULPING STEP, A FINELY DISPERSED GAS CONTAINING FREEGASEOUS OXYGEN AND RECOVERING SAID VANILLIN PRODUCT, SAID ALKALINEPULPING LIQUOR CONTAINING AS THE SOLE ESSENTIAL COMPONENTS, WATER AND ANALKALINE PULPING REAGENT SELECTED FROM THE GROUP CONSISTING OF SODIUMHY-